1. Field of the Invention
This disclosure relates to a building drum for the manufacture of tires.
The disclosure relates more particularly to a building drum having shoulders on which the bead wire or bead wires are deposited in the course of assembly through a lateral approach towards the said shoulders. Through such a drum, different rubber-based plies, including a carcass ply, can be placed in succession on the outer receiving cylindrical surface and bead wires and semi-finished products or profiled elements based on a rubber mixture can be positioned on the shoulders located in the vicinity of the axial extremities of the receiving surface and held there assembled, together with the rubber-based plies previously positioned and folded back at the shoulders. The bead wires and the semi-finished products are held against the shoulder by adhesively bonding the products together.
Because the carcass formed upon it shrinks from the drum, the circumference of the drum has to be reduced to release the carcass and ensure that there is release between the outer circumference of the drum and the inner circumference of the carcass. The drum must therefore be radially retractable so that the green tire so assembled can be withdrawn. Such a drum generally comprises a plurality of segments which can move radially between a deployed or working position of the drum and a retracted position. In addition to this, some tire carcasses have inclined shoulders which also make it necessary for segments to be withdrawn axially.
2. Related Art
Thus publication WO 02/053355 in the name of the applicants describes such an expandable building drum with inclined shoulders. The building drum comprises a body mounted to rotate on a central shaft, comprising a cylindrical assembly surface formed of several shoulder segments. The segments are circumferentially adjacent, they are provided with covering plates to ensure an outer surface of circular shape, and are mounted so that they can move radially and axially between an expanded position of the drum and a retracted position of the drum. One disadvantage of this drum is the use of vacuum valves connected to a pneumatic circuit with a view to ensuring that the components are held at the shoulders, which requires an additional feed source, complicates construction of the drum and renders operation less reliable. Another disadvantage of such a drum relates to activation of the segments, which is brought about through a connecting rod that follows the profile of a cam in the deployed position, return to the retracted position being brought about by a resilient membrane enveloping the segments, which gives rise to concerns about reliability as the membrane wears or ages. In addition to this, the drum comprises many segments, which increase in number with the difference in diameter between the working and retracted positions of the drum. Because of this, this drum is not suitable for building small diameter carcasses, or those having a significant difference between the diameter of the outer cylindrical surface and the diameter measured at the beads thereof.
One solution has been described in document FR 2 509 663 in which the drum comprises two different groups of segments, of the keystone and voussoir type, arranged successively in a circumferential direction. The segments are mounted so as to move between a deployed position of the drum, in which all the segments are circumferentially adjacent, and a retracted position of the drum in which the segments are radially offset and retracted. Each segment is connected by articulated arms, activating a central slide which can move axially, two coaxial slides being provided within the drum, one connected to the keystone segments and the other to the voussoir segments. The drum also comprises means for moving the slides.
The shoulders are connected to the arms activating the segments via a mechanism with a rack and toothed sector, a mechanism which ensures that they move axially in relation to the segments and at the same time, so that the green tire built on the drum can be removed. Adjustment of all the racks to achieve segments which are concentric and parallel to the axis of the drum proves to be difficult.
In a variant the drum comprises shoulders mounted so as to be articulated on the segments. Each shoulder is mounted using a tie rod, which is articulated on an articulated element mounted with a tension spring in relation to the segment. The articulated element is activated by means of a toothed sector on an activating arm of a segment which engages an articulated cam and which pushes the shoulder tie rod outwards in the deployed position of the drum. Such a tensile spring solution gives rise to reliability problems if the spring should jam or break.
As the shoulders are kinematically connected to the segments, radial movement of the segments simultaneously brings about movement of the shoulders, either in an axially sliding direction or pivoting about an axis perpendicular to the axis of the drum, to release the shoulders with respect to the parts forming the bead of the green tire.
However the mechanism activating the segments and shoulders of the drum according to this document is complex and bulky, which has consequences for the dimensions, reliability and cost of the drum. In addition to this, because of the large number of articulated parts of which the drum is made up, significant chatter and operating play have to be taken into account, play which becomes greater as the mechanisms wear.